Medical devices to be inserted into a living body, such as catheters, guide wires, indwelling needles and the like, can exhibit good lubricity in order that damage to tissue such as blood vessels is reduced and handleability of an operator is improved. Hence, there have been developed and put into practice methods of coating a base material surface with a hydrophilic polymer having lubricity. In such medical devices, elution and peeling-off of the hydrophilic polymer from the base material surface presents a problem in maintaining safety and handleability.
In order to avoid such a problem, Japanese Patent Laid-Open No. Hei 8-33704 discloses a medical device wherein a water-soluble or water-swelling polymer is dissolved in a solvent capable of swelling a base material of the medical device to prepare a polymer solution, and the base material of the medical device is swollen by immersion in the polymer solution, followed by crosslinking or converting the polymer into a higher molecular weight product on the base material surface thereby forming a surface lubricating layer on the base material surface.
In the method described in the above-indicated Japanese Patent Laid-Open No. Hei 8-33704, the surface lubricating layer can be strongly fixed on the base material to some extent. Especially, where the base material per se is swollen with a hydrophilic polymer solution, very strong fixing is enabled by the formation of an interpenetrating network structure of the base material polymer and the hydrophilic polymer formed as the surface lubricating layer. On the other hand, where the base polymer is unlikely to be swollen with a hydrophilic polymer solution, the hydrophilic polymer serving as the surface lubricating layer is fixed to the base material only by the insolubilizing effect, involving a higher risk that the surface lubricating layer is peeled off when compared with the polymer base material forming the interpenetrating network structure. Thus, there is a need for a coating method wherein a hydrophilic polymer can be fixed more strongly on a sparingly swelling polymer base surface.
For a method of strongly fixing a hydrophilic polymer on a polymer base surface in large amounts, Japanese Patent Laid-Open No. 2007-289299 discloses a medical device, which includes a polymer material serving as a base layer and having a first higher-order structure in the molecule and a first functional group provided at least at one terminal of the first higher-order structure, and a hydrophilic polymer having, in the molecule, a second higher-order structure capable of interacting with the first higher-order structure and a second functional group capable of hydrogen bonding with the first functional group and provided at least at one terminal of the second higher-order structure.
However, the method set out in the above-mentioned Japanese Patent Laid-Open No. 2007-289299 has a problem in that limitation is placed on the combination of a base polymer and a hydrophilic polymer.